December 2012: NSA contract worker Edward Snowden sends an anonymous email to Glenn Greenwald. Greenwals is at this point a journalist at online-only outlet Salon. Snowden says that he has documents to share, but only via encrypted email. Greenwald ignores this initial approach.

January 2013: Snowden approaches American documentary film-maker Laura Poitras, due to his awareness of Poitras' production of a film investigating U.S. government surveillance. Snowden asks Poitras to work with Glenn Greenwald on the documents he intends to leak.

Late March–early April: Greenwald and Poitras meet to discuss Snowden. Greenwald prioritizes the story and begins dealing directly with Snowden, in secret.

June 1: Greenwald (who is now working for Guardian USA, Poitras, and Guardian reporter Ewen MacAskill travel to Hong Kong to meet Snowden.

June 5: The first Guardian exclusive from Snowden's material is published: a front page article revealing that the U.S. government issued a secret court order requiring that telecom firm Verizon hand over phone metadata from several million Americans.

June 6: The Washington Post publishes a website article by Barton Gellman and Laura Poitras about the NSA's Prism program, based on material leaked by Snowden. This reveals that the NSA was granted access to the personal data of users of a wide range of technology and social networking companies, including Facebook, Google, Skype, Microsoft, and Apple. Just twenty minutes later, the Guardian publishes its own version of the Prism revelations to the Guardian website in the form of an article by Glenn Greenwald and Ewen MacAskill which also records the technology companies' denials.

June 7: The Guardian updates its Prism story from the day before and adds that Britain's GCHQ has also been able to access user data from the named U.S. technology companies via a reciprocal agreement with the NSA.

June 8: The next Snowden leak reveals the existence of a technology program named "Boundless Informant," which enables the NSA to record and analyze internet data and its sources. This apparently contradicts the NSA's assurances that it was unable to comprehensively manage all of the data it collects.

June 9: The Guardian reveals Snowden's identity for the first time, in a video interview filmed by Laura Poitras which is posted on its website.

June 10: Snowden reportedly checks out of his Hong Kong hotel and begins a campaign to seek asylum in a country without an extradition agreement with the United States. Meanwhile, the British news organization, the Mail Online publishes photographs of Snowden's partner, a dancer named Lindsay Mills. The photographs, some of which feature Mills in underwear, are taken from what is at that stage the publicly-accessible archive of her personal blog, L's Journey. The following day, the blog is no longer available, though Mills' Twitter account remains online, if inactive.

June 12: Hong Kong's South China Morning Post publishes an interview with Snowden, the first since the whistleblower went public. This reveals that the NSA has been routinely hacking Chinese and Hong Kong computers since 2009.

June 16: The Guardian reports that GCHQ intercepted foreign ministry politicians' communications at the London G20 summit in 2009.

June 17: The Guardian organizes a "crowd-sourced" online Q&A with Snowden (who is by now at a secret location and evading the U.S. authorities) using the Twitter hashtag #AskSnowden and the news organization's in-house online commenting platform.

June 20: The Guardian publishes further leaked information revealing that U.S. judges agreed court orders enabling the NSA to use data "inadvertently" gathered from U.S. communications, without a warrant.

June 21: The Guardian reveals that GCHQ has secured access to the backbone fiber cable network delivering global phone and internet data; also that GCHQ is storing and analyzing large quantities of data shared with the NSA.

June 21: The United States charges Snowden with two felonies under the Espionage Act and issues a request that the Hong Kong authorities detain him. The Hong Kong administration claims that the U.S. charges have no force in Hong Kong law.

June 23: Snowden leaves Hong Kong for Moscow. Meanwhile WikiLeaks issues a statement claiming it is assisting him in his bid for political asylum.

June 25: President Obama issues a statement confirming plans to extradite Snowden to the United States. Russian foreign minister Sergei Lavrov claims Snowden did not cross the border into Russia.

July 1: Russia reveals that Snowden has applied for asylum there. WikiLeaks issues a statement detailing a further twenty countries to which Snowden has applied for asylum, including France, Germany, Ireland, China, and Cuba.

July 3: President Morales' plane is forced to land in Vienna while en route from Moscow to Bolivia after a number of European countries refuse it airspace. This is owing to the suspicion Snowden is on board and is being transported to Bolivia. Venezuela, Argentina, Ecuador, Uruguay, and Bolivia denounce the treatment of Morales, who is held in Vienna airport for 12 hours while his plane is searched. Bolivia files a complaint to the United Nations. UN secretary general Ban Ki-moon issues a statement arguing that Snowden acted inappropriately by leaking details of NSA surveillance.

July 5: After initially publishing stories based on Snowden's leaked material, the Washington Post now claims Snowden should be prevented "from leaking information that harms efforts to fight terrorism and conduct legitimate intelligence operations."

July 8: A second video interview with Snowden is released by the Guardian. The video reinforces Snowden's criticism of unaccountable state surveillance as the driving force in his decision to leak the documents.

July 12: The Guardian publishes a further article revealing that Microsoft granted the NSA "pre-encryption stage" access to its online email platform Outlook.com and to Skype video calls.

July 12: Snowden holds a press conference at Moscow's Sheremetyevo airport, where he announces he will be applying for temporary asylum in Russia while he applies for permanent asylum in a Latin American country.

August 1: Snowden leaves Sheremetyevo airport to take up a year's temporary asylum in Russia.

August 12: Barack Obama establishes a Review Group on Intelligence and Communications Technologies to examine "how in light of advancements in communications technologies, the United States can employ its technical collection capabilities in a manner that optimally protects our national security and advances our foreign policy while respecting our commitment to privacy and civil liberties, recognizing our need to maintain the public trust, and reducing the risk of unauthorized disclosure."

August 19: Journalist Glenn Greenwald's partner, David Miranda, is detained under anti-terrorism legislation while walking through London Heathrow airport en route to Brazil after visiting journalist Laura Poitras in Berlin. Miranda's computers, mobile phones, and data storage devices are confiscated.

August 20: The Guardian editor Alan Rusbridger reveals that on July 20 officials from GCHQ entered the news organization's headquarters in London and insisted that the computers holding the leaked NSA documents be destroyed with the use of power tools. Guardian staff—who made it clear that digital copies of the documents had already been transferred to Brazil and the United States—destroyed the hard drives and memory chips of a MacBook computer in the presence of the GCHQ officials. Photographs of the wrecked computer are uploaded to the Guardian's website and, in January 2014 video of the event will emerge in an article published to promote the Guardian's book about the Snowden leak.

August 23–25: The Guardian announces a partnership with the New York Times and the nonprofit investigative news organization, ProPublica, to work together on the Snowden documents.

September 5: The Guardian, the New York Times and ProPublica jointly publish a further article revealing an NSA and GCHQ program called "Sigint [signals intelligence] enabling" which involves the agencies co-operating with companies to "insert vulnerabilities into commercial encryption systems." It becomes clear that the NSA has been working on "backdoors" to internet encryption algorithms that are widely used to secure personal and commercial online transactions around the world.

October 4: The Guardian publishes a new article revealing that the NSA has hacked the Tor browser bundle—a piece of software popular among human rights activists because it enables users to browse the internet anonymously.

October 15: Glenn Greenwald leaves the Guardian to establish his own news organization in collaboration with eBay founder and entrpreneur Pierre Omidyar.

October 17: The British House of Commons Home Affairs Select Committee launches an investigation into the potential security risks posed by the Guardian's articles.

October 23: German Chancellor Angela Merkel calls President Obama to gain assurances that her personal cellphone had not been hacked by the NSA, following an article in news magazine Der Spiegel alleging that this was the case. The article is based on documents leaked by Snowden.

October 30: The Washington Post reports on a joint NSA and GCHQ project named "Muscular" which allows the agency to intercept and decrypt personal data that flows between the open internet and Google and Yahoo's cloud services.

October 31: NSA Director Keith Alexander alleges that Snowden may have taken more than 200,000 secret documents when he left the agency.

November 1: Snowden publishes a "Manifesto for the Truth" in Der Spiegel justifying his leaks on the grounds that they sparked a global debate about the accountability of digital surveillance.

December 3: Guardian editor Alan Rusbridger appears before the House of Commons Home Affairs Select Committee to answer questions on whether publishing the Snowden leaks posed a threat to British national security.

December 18: Barack Obama's Review Group on Intelligence and Communications Technologies publishes a 300-page report calling for substantial reform to the NSA and the judicial processes surrounding it.

January 17, 2014: Obama announces a package of small but significant reforms to the gathering of communications data, while also calling upon Congress to conduct further reviews.

April 14, 2014: The Guardian and the Washington Post are both awarded the Pulitzer Prize for public service journalism for their coverage of the Snowden leak.

NoteThis chronicle has been compiled from sources that were publicly available as of April 2014. The most comprehensive timeline of the earlier Snowden leak news events is hosted at the user generated news website Reddit. A full and easy to navigate timeline can also be found on the Al Jazeera America site. The Guardian's own chronicle is a useful source, particularly for the early phases of The NSA Files during the summer of 2013. Peter Maass' (2013) piece for the New York Times provides helpful background information on how Glenn Greenwald, Ewen MacAskill, and Laura Poitras handled Snowden and the first round of leaks: "How Laura Poitras Helped Snowden Spill His Secrets." As we completed this paper the Guardian duplicated its earlier approach with WikiLeaks and published its own insider book authored by Luke Harding (2014). Though we have used it with care, we have found this book to be a valuable primary source.

Please feel free to email corrections, clarifications, and additions to this chronicle to us and we will endeavor to include them.

Andrew Chadwick and Simon Collister, September 2014

New Political Communication Unit, Royal Holloway, University of London.